1. Field of the Invention
This invention relates to a printing system which records or erases a visible image, with a recording device such as a thermal head, onto or from a recording medium capable of repeated recording or erasing of a visible image by clouding or clarifying the image through the application of thermal energy.
2. Description of the Related Art
Conventional hard copies provide a permanent record of images by externally applying developer (e.g., ink or toner) to a recording medium (e.g., paper) to form an image, or by forming a recording layer on a substrate (e.g., paper) like thermosensitive recording paper and forming a visible image in the recording layer.
As a greater variety of information networks have recently been developed and more and more facsimile machines and copiers are now being used, the consumption of recording mediums has been increasing rapidly, leading to environmental destruction problems including forest destruction and social problems such as waste disposal. To cope with those problems, there is a great demand for the recycling of recording paper and the reduction of recording paper consumption. Therefore, a recording medium allowing repeated recording and erasing has been attracting attention these days.
For recording mediums with such properties, a recording medium has been proposed which changes reversibly from a transparent state to a cloudy state, depending on the temperature applied to the recording medium, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 55-154198.
For example, when such a recording medium in a cloudy state is heated from room temperature to a first threshold temperature, the medium changes from the cloudy state to a transparent state, and remains transparent even after it has dropped back to room temperature. When the temperature of the recording medium is raised from room temperature through the first threshold temperature to a second threshold temperature, the medium goes into a cloudy state, and remains cloudy even after it has dropped again to room temperature. These changes can be reproduced repeatedly.
A study of degradation of the resolution in repeatedly recording onto such a recording medium with a thermal head, has been reported, for example, in "Proceedings of 4th Japanese Symposium on Non-impact Printing Technologies Symposium," 3-2, p. 57, 1987.
Further, a display changing apparatus has been proposed which records and erases information onto and from a displaying medium having a thermally reversible recording material, as disclosed in, for example, Jpn. UM Appln. KOKAI Publication No. 2-19568. This apparatus contains an erasing device for thermally erasing the records from the displaying medium, and a thermal printing device. This publication discloses an apparatus which erases the thermally reversible display on the floppy disk cartridge with a heater head (the erasing means), and writes the display with a moving thermal head (the printing means).
Further, in Jpn. UM Appln. KOKAI Publication No. 2-3876, another apparatus has been disclosed which records and erases the information onto an information recording card having a thermally reversible recording layer by means of a heat roller (the erasing means) and a thermal head (the printing means).
Still further, in Japan Hardcopy '90, NIP-2, p. 147, 1990, a recording material has been announced which uses leuco dye as a coloring source whose color changes reversibly only under the control of thermal energy.
As mentioned above, a recording method using a recording medium capable of repeated recording and erasing solves the problems encountered with conventional recording methods. As conventionally accomplished, a recording medium made up of a low-molecular/high-molecular composite film alternating between a cloudy and a transparent state, depending on the heating process as mentioned above, is an excellent material which enables a recording and an erasing operation with a thermal head.
In such systems, however, the effect of ambient temperature cannot be ignored. When a visible image is recorded or erased in the open air, there may be a seasonal temperature difference of nearly 30.degree. C.
Therefore, even if a thermal head is simply electrically energized to rise to the clouding temperature or the clarifying temperature, the head cannot be heated to the desired temperature without consideration of the effect of the ambient temperature on the system.